1. Field of the Invention
The present invention is a detector array and associated signal processing system for incorporation into an electro-optical tracking loop.
2. Description of the Prior Art
The generalized tracking problem requires a system to acquire a target anywhere within a relatively wide field of view (FOV); to measure the offset between the target's position and the tracking position's boresight; to predict the position of the target at the time of the next pulse, and to drive the pointing system to this location. As this process is repeated, the offset becomes progressively smaller and the precision of the measurement consequently must become more accurate. This system to be successful, must converge on the target rapidly. The magnitude of the offset between the target angle and the boresight must decrease rapidly and must remain below a prespecified pointing error tolerance for an interval of time.
The tracking process initially requires relatively coarse offset measurements over a relatively wide field of view. As the tracking process proceeds, more precise measurements are required over smaller fields of view. Also, there are occasions when the system will be forced to "backtrack" to a wider field of view (during violent target acceleration or during target obstruction by physical interference).
Thus, a system which has the capacity to make coarse measurements over a wide field of view and more precise measurements over a narrow field of view simultaneously is preferable to a system which "zooms in" on the target as the tracking loop is closed.
There have been two main classes of detector arrays used in tracking loops, those which continuously monitor the output of each pixel with a high bandwidth amplifier and those which integrate the returns over an exposure period and output them sequentially. When a pulsed illuminator is used in the active systems, high bandwidth signal processing provides the following advantages: bandwidth of the receiver signals may be matched to that of the anticipated return to maximize the rejection of noise and the low bandwidth clutter; range may be effectively measured; a range dependent threshold may be set up for detection; and the time lag of the sequential readout is eliminated.
As shown in FIG. 1 of this application, a prior art passive electro-optical tracking loop is composed of the following subsystems: a receiver telescope, a detector array situated in the focal plane of the receiver telescope which measures the angular displacement of one or more targets in its field of view with respect to its boresight and a signal processing system which translates the outputs of the detector array into pointing angle commands.
The specific example has in FIG. 1, two receiver telescope means used to identify the targets. One receiver telescope means will identify the target and direct the optical energy reflected from the target or emitted from it (as would be in infrared radiation) to the fine track-detector array. The fine track detector array in turn would convert the optical energy received from the target into electrical energy.
This electrical energy would then input into the signal processing system fine track. Parallel to the fine track signal processing system would be a separate coarse track detector element which would be utilized to perform a coarse track reception of optical energy reflected or emitted from the target. Both the fine track and the coarse track are two separate parallel paths of receptors for optical energy from the target and both receptor paths have their own independent receiver telescope means. The integration of the fine track and the coarse track signal processing information is performed in the fine track/coarse track signal processing algorithms. As can be seen in cross section I.sub.A --I.sub.A and cross section I.sub.B --I.sub.B, the fine track and coarse track focal plane arrays would be comprised of varying numbers of quadrants. The fine track quadrants would have a minimum of four quadrants while the coarse track elements would number more that four.
FIG. 2 of this application demonstrates the use of a beam splitter and only one receiver telescope means to achieve the same effect as the parallel path receiver telescope means of FIG. 1. This is a passive system where the target will emit or reflect energy to the receiver telescope means. The receiver telescope means comprises a convex and concave lens on a common colinear axis. The optical energy passing through the sole receiver telescope means strikes a beam splitter. A beam splitter is a selectively transmissive reflective means which permits a predetermined portion of the optical energy to pass through it to the fine track focal plane array and another predetermined portion of the optical energy to pass through a second convex lens to the coarse track detector array.
Again, the fine track and coarse track detector arrays will convert the optical energy to electrical impulses which will be transmitted to the fine track and coarse track signal processing algorithms. Cross section II.sub.A --II.sub.A demonstrates the fine track detector array and cross section II.sub.B --II.sub.B demonstrates the coarse track detector array. This system is again a passive system meaning that there is no energy generated within this system and sent to strike the target where it is reflected back into the receiver telescope means.
A generic active electro-optical tracking loop would be composed of: a pulsed laser illuminator, a receiver telescope, a detector array situated in the focal plane of the receiver telescope which again would measure the angle of displacement of one or more targets in its field of view with respect to its boresight and a signal processing system which would translate the outputs of this detector array and to pointing signal commands. The active electro-optical tracking loop would utilize the pulse laser illuminator to direct a beam of optical energy to the moving target. This energy would either enter the receiver telescope means directly as in a direct reflection or the optical energy from the pulse laser illuminator would be reflected to a reflective means which in turn would reflect that optical energy into the receiver telescope.
The example of prior art as shown in FIGS. 1 and 2 are exemplary of the many examples that can found used currently for electro-optic tracking loop systems. The electro-optic tracking loop therefore as seen in the prior art utilizes either one or two receiver telescopes and must use two distinct detector element arrays, one for fine track and one for coarse tracking, with distinct and separate coarse track and fine track signal processing.
The patent to Fellman, U.S. Pat. No. 3,993,888, dated Nov. 23, 1976 is noted for its disclosure of an image processing device using a photodiode detector array consisting of a circular central element surrounded by 24 radial elements. A digital logic signal is produced which is the binary representation of the portion of the image centered on the array.
The patent to Beck et al., U.S. Pat. No. 4,398,408, dated July 12, 1983 is further noted for its disclosure of an opto-electronic device in which the array of the detectors comprises a plurality of detectors extending from the optic axis of the device and signals delivered by the array are processed through a transcribing synchronizing circuit for causing a pair of cartesian coordinants to correspond sequentially to each pair of coordinants.
Finally, the patent to Walker et al., U.S. Pat. No. 4,191,957, dated Mar. 4, 1980 is additionally noted for its disclosure of a method of processing range doppler data using a polar recording format.
The problem to be solved is the efficient detection of target images utilizing a common detector array in which all sub-boundaries are either concentric circles or radii emanating from the common origin of the circles with a combination of concentric fine track and coarse track arrays used on a single focal plane. And, a combined coarse track fine track signal processing algorithm to simplify and eliminate additional components in the optical tracking system.